As shown in FIG. 1, a bicycle crank axle 1A of the prior art is provided respectively on both ends thereof with a threaded portion 2A engageable with a bearing 3A which is fastened with the outer end of the frame tube 6A by means of a washer 4A and a fastening nut 5A.
Such a prior art crank axle 1A as described above is defective in design in that the crank axle 1A is rather complicated in construction, and that the threaded portion 2A of the crank axle 1A is highly vulnerable to damage or jamming, and further that the crank axle 1A can not be made economically.